%I
%S 2,3,5,10,15,23,34,37,47,70
%N Numbers m such that 6^m  m is a semiprime.
%C From _Robert Israel_, Sep 06 2016: (Start)
%C Even n is in this sequence iff (6^nn)/2 is prime.
%C 3*k is in this sequence iff (2*6^(3*k1)k is prime.
%C Also contains 275, 278 and 683.
%C The only other possible member less than 275 is 259. (End)
%e 2 is in this sequence because 6^22 = 2*17 is semiprime.
%e 10 is in this sequence because 6^1010 = 2*30233083 and these two factors are prime.
%p Res:= NULL:
%p for n from 1 to 100 do
%p F:= ifactors(6^nn, easy)[2];
%p if add(t[2], t=F) >= 3 or (hastype(F, symbol) and add(t[2], t=F) >= 2)
%p then flag:= false
%p elif add(t[2], t=F) = 2 and not hastype(F, symbol) then flag:= true
%p else
%p flag:= evalb(numtheory:bigomega(6^nn)=2)
%p fi;
%p if flag then Res:= Res, n fi
%p od:
%p Res; # _Robert Israel_, Sep 06 2016
%t Select[Range[90], PrimeOmega[6^#  #]== 2&]
%o (MAGMA) IsSemiprime:=func<i  &+[d[2]: d in Factorization(i)] eq 2>; [m: m in [1..90]  IsSemiprime(s) where s is 6^mm];
%Y Cf. similar sequences listed in A252656.
%K nonn,more
%O 1,1
%A _Vincenzo Librandi_, Dec 21 2014
